Impulse oscillometry bronchodilator response in preschool children

Abstract Background In preschoolers, performing an acceptable spirometry and measuring bronchodilator response (BDR) is challenging; in this context, impulse oscillometry (IOS) represents a valid alternative. However, more studies on the standardization of BDR for IOS in young children are required. Objective The objective of the study was to identify optimal thresholds to define a positive BDR test with IOS in preschoolers with suspected asthma. Methods Children aged 3–6 years with suspected asthma and their lung function investigated with both IOS and spirometry pre‐ and post‐BDR were retrospectively analyzed. The spirometric BDR was defined as positive when the change of FEV 1 was ≥12% or ≥200 mL. The oscillometric BDR was defined as positive in case of change of at least −40% in R5, +50% in X5, and −80% in AX. Results Among 72 patients, 36 (age 5.2 ± 1 years; 64% boys) were selected for the subsequent analysis according to ATS/ERS quality criteria of measurements; specifically, 19 patients did not meet IOS and 36 did not meet spirometry criteria. The spirometric BDR was found positive in seven subjects (19.4%); conversely, a positive oscillometric BDR was identified in four patients (11.1%). No patient presented a positive BDR response with both methods. In IOS, the mean decrease in R5 and AX was 19.9% ± 10% and 44% ± 22.1%, and the mean increase in X5 was 23.3% ± 17.8%, respectively. A decrease in R5 of 25.7% (AUC 0.77, p = .03) and an increase in X5 of 25.7% (AUC 0.75, p = .04) showed the best combination of sensitivity and specificity to detect an increase of FEV 1 ≥ 12% and/or ≥200 mL. Conclusion The IOS represents a valid alternative to spirometry to measure BDR in preschool children and should be the gold standard in this age group. We are considering a decrease of 26% in R5 and an increase of 26% in X5 as diagnostic threshold for BDR.